1. Field of the Invention
The present invention relates to surgical instrumentation and, more particularly, pertains to a surgical instrument and a method for positioning and guiding a drilling tool.
2. Description of the Prior Art
It is well known to drill holes in bones in order to accommodate fastening devices used to anchor implants within a patient""s body. For instance, over the last few years, pedicle screws have been used to anchor internal instrumentation systems to the spinal column of patients for correcting a variety of spinal disorders. There are many advantages of using such pedicles screw as compared to conventional anchoring devices, such as hooks, but the risks associated with their implantation into the vertebral column of the patients have limited their universal acceptance.
Commonly used technique for inserting a pedicle screw requires the preparation of a pilot hole through the pedicle before inserting the screw therein. Typically, the selection of the insertion point is made from anatomical techniques or a preoperative CT scan. The preoperative CT scan can be used for determining the angle of insertion, as well as for screw length and diameter. It is also known to use intra-operative X-rays or fluoroscopic guidance before pedicle hole preparation to assess the appropriate size and placement of the pedicle screws. After an appropriate pedicle has been selected, an initial small puncture through the posterior cortex can be made to mark the insertion point and to facilitate the drilling procedure. Then, the pilot hole is usually made with a drill bit or a pedicle probe. Before inserting the screw in the pilot hole, the latter is manually probed in order to check for violation of the pedicle walls. It is noted that the screw length can be determined by the use of a calibrated probe inserted into the pedicle pilot hole. Intra-operative X-rays or fluoroscopy can be used to verify the accuracy of the pilot hole or the screw.
It is also known to form individual templates customized on the basis of three-dimensional reconstruction of the bone structure extracted from CT image data in order to provide preoperative surgical planning.
Electrical methods and saline injection technique have been developed to confirm the correct path of the pilot hole prior to pedicle screw insertion.
Computer-assisted guidance systems have also been developed in order to visually track the intra-operative position of the vertebra during pedicle screw insertion.
In a further attempt to prevent misplacement of the pedicle screws, it has been proposed to use a guide to provide a safe route for drilling a pilot hole. U.S. Pat. No. 4,907,577 issued on Mar. 13, 1990 to Wu discloses a spinal transpedicle drill guide having a I-shaped body, a guiding base and a positioning base which are slidable in a transversal direction on the I-shaped body to prevent deviation of the drilling direction in the transversal plane of the vertebra of the pedicle. However, this guide does not allow for adjustment of the drilling path in the lateral plane of the vertebra.
It is therefore an aim of the present invention to provide a surgical guiding instrument which can be used to properly orient a drilling axis.
It is also an aim of the present invention to provide a surgical guiding instrument which is adapted to allow for safe insertion of a screw into a bone.
It is a further aim of the present invention to provide a surgical guiding instrument which is relatively simple and economical to manufacture.
It is a still further aim of the present invention to provide a kit adapted to orient and guide a drilling tool relative to a bone of a patient.
It is still a further aim of the present invention to provide a method for safely preparing a pilot hole in a pedicle of a selected vertebra of a patient""s spinal column.
Therefore, in accordance with the present invention there is provided a surgical guiding instrument for use with a drilling tool, comprising a support, a bone engaging element adapted to be mounted on said support and having a tip portion for engaging a region of a bone to hold the support in a specific orientation with respect thereto, a drill guide mounted to said support and having a passage defining a drilling axis extending by the tip portion of said bone engaging element in a non-intersecting manner in the plane of said support so as to define a gap, at least one of said drill guide and said bone engaging element being adjustably movable relative to said support to provide for the increase or reduction of said gap in accordance with a diameter of the bone at a section thereof to be engaged by said bone engaging element.
In accordance with a further general aspect of the present invention, there is provided a kit for orienting and guiding a drilling tool relative to a patient""s bone, comprising a support, a bone engaging element adapted to be mounted on said support for engaging a region of a bone to orient the support with respect thereto, and a drill guide adapted to be mounted to said support and defining a passage for guiding said drilling tool along a drilling axis during use, said drill guide being angularly adjustable relative to said bone engaging element in the plane of said support, thereby providing for adjustment of the angular orientation of the drilling axis in the plane of the support, and wherein said drill guide is adjustably rotatable about an axis of rotation perpendicular to said drilling axis,
In accordance with still a further general aspect of the present invention, there is a method for preparing a pedicle pilot hole in a pedicle of a selected vertebra with a drill positioning guide having an elongated support on which a pedicle finder and a drill guide are mounted, wherein the drill guide defines a drilling axis extending by the tip portion of said pedicle finder in a non-intersecting manner in the plane of the support so as to define a gap, the method comprising the steps of
a) adjusting the gap in accordance with the diameter of the pedicle in which a pilot hole has to be defined,
b) engaging the tip portion of the pedicle finder with the pedicle in order to angularly align the support and the drill guide with the pedicle in a transversal plane of the vertebra,
c) adjusting the position of the drill guide on the support so that the drilling axis be aligned with a predetermined insertion point on a posterior surface of the pedicle in order to angularly align the support and the drill guide with the pedicle in a lateral plane of the selected vertebra, and
d) drilling the pedicle pilot hole in the pedicle with the drilling tool extending through the drill guide along the drilling axis thereof.
Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which:
FIG. 1 is perspective view of a surgical guiding instrument used in connection with a pedicle finder to guide a drilling tool in accordance with a first embodiment of the present invention;
FIG. 2 is a lateral view of a portion of a spinal column illustrating how the surgical guiding instrument is used to guide the drilling tool in order to drill a pilot hole in a pedicle of a selected vertebra;
FIG. 3 is a side elevational view of the surgical guiding instrument;
FIG. 4 is a cross-sectional view taken along line 4xe2x80x944 in FIG. 3;
FIGS. 5a and 5b are schematic views illustrating possible drilling paths for two different positions of the pedicle finder relative to the surgical guiding instrument;
FIG. 6 is an enlarged elevational view of the surgical guiding instrument illustrating a variant of the present invention wherein the guiding sleeve used to guide the drilling tool is freely rotatable in the plane of the surgical guiding instrument;
FIG. 7 is a cross-sectional view taken along line 7xe2x80x947 in FIG. 6;
FIG. 8 is a cross-sectional view taken along line 8xe2x80x948 in FIG. 7;
FIG. 9 is a cross-sectional view taken along line 9xe2x80x949 in FIG. 3; and
FIG. 10 is a schematic lateral elevational view of a second embodiment of the present invention.